CHICAGO (AP) — The Chicago Cubs, scuffling and inconsistent since winning the World Series, acquired ace Jose Quintana from the White Sox on Thursday in a major trade between crosstown rivals.

Trailing Milwaukee by 5 1/2 games in the NL Central at 43-45, the Cubs shook things up in a big way by acquiring Quintana, a 2016 All-Star. In exchange, the Cubs sent four prospects to the rebuilding White Sox: outfielder Eloy Jimenez, right-handed pitcher Dylan Cease, and infielders Matt Rose and Bryant Flete.

Quintana, a lefty, is 4-8 with a 4.49 ERA in 18 starts this season. He won a career-high 13 games last season with a personal-best 3.20 ERA while making his first All-Star team and is 50-54 with a 3.51 since debuting with the White Sox in 2012.

Quintana has pitched better lately after a slow start and is under club control through 2020.

"He's a true professional who had to deal with everything from poor run support to the bullpen occasionally letting him down, the defense letting him down," White Sox general manager Rick Hahn said. "He certainly never complained, never threw his arms up in the air, never rolled his eyes, never expressed any displeasure with his teammates. Instead, he was always supportive and continued to go about his business and set a wonderful example for the other young players in our clubhouse.

"Frankly, the call to Jose this morning was one of the more difficult ones I've made."

The Cubs were looking to boost a rotation that ranks 17th in the majors in ERA. It turns out help was only a few miles from Wrigley Field, and the starters certainly could use a boost.

Ace Jon Lester got pounded for 10 runs in two-thirds of an inning in his most recent start against Pittsburgh. Jake Arrieta, the 2015 NL Cy Young Award winner, has been inconsistent. Kyle Hendricks has been sidelined since June 4 because of tendinitis in his right hand, and John Lackey has a 5.20 ERA.

Hahn said he and Cubs president of baseball operations Theo Epstein exchanged text messages shortly after the draft. There wasn't much communication between them until Hahn reached out on Sunday.

Hahn told Epstein at that point any trade would have to involve Jimenez and Cease. Talks heated up over the next few days before the teams agreed to a blockbuster deal.

The White Sox, who were close to trading Quintana in the offseason, continue to load up on young players. They started to rebuild after four straight losing seasons last winter when they traded All-Star pitcher Chris Sale to Boston and outfielder Adam Eaton to Washington. They acquired two of baseball's top prospects in return, getting second baseman Yoan Moncada from the Red Sox and right-hander Lucas Giolito from the Nationals.

The White Sox also signed prized Cuban prospect Luis Robert to a minor league deal in May.